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3 guesses to Swimmer’s Solution

  • Ryver

    48 mins
    ~~~~~
    ~~~~
    Algebra time!
    Let R = Phelps’ speed at still water
    Let S = effect of the stream to his speed

    2 = 40(R+S) = 60(R-S)
    40R + 40S = 60R – 60S
    100S = 20R
    5S = R

    2 = 2/3 of an hour x (R+S)mph
    2 = 2/3 x(6S)
    2 = 4S
    S = 0.5 mph

    R = 2.5 mph

    2/2.5 = 0.8 hours or 48 mins

  • Nailed it, Ryver. Great job!

    Michael Phelps speed = X km/minute
    Lake current speed = Y km/minute

    2/(X+Y) = 402/(X-Y) = 60

    Solving the simultaneous equations gives X = 1/24

    Therefore, to cover 2km will take 2/X = 48 minutes

    You’re today’s winner.